This invention relates to compositions and methods for catalytically bleaching substrates with atmospheric oxygen and a peroxyl species, using a metal-ligand complex as catalyst.
Peroxygen bleaches are well known for their ability to remove stains from substrates. Traditionally, the substrate is subjected to hydrogen peroxide, or to substances which can generate peroxyl radicals, such as inorganic or organic peroxides. Generally, these systems must be activated. One method of activation is to employ wash temperatures of 60xc2x0 C. or higher. However, these high temperatures often lead to inefficient cleaning, and can also cause premature damage to the substrate.
A preferred approach to generating peroxyl bleach species is the use of inorganic peroxides coupled with organic precursor compounds. These systems are employed for many commercial laundry powders. For example, various European systems are based on tetraacetyl ethylenediamine (TAED) as the organic precursor coupled with sodium perborate or sodium percarbonate, whereas in the United States laundry bleach products are typically based on sodium nonanoyloxybenzenesulphonate (SNOBS) as the organic precursor coupled with sodium perborate.
Precursor systems are generally effective but still exhibit several disadvantages. For example, organic precursors are moderately sophisticated molecules requiring multi-step manufacturing processes resulting in high capital costs. Also, precursor systems have large formulation space requirements so that a significant proportion of a laundry powder must be devoted to the bleach components, leaving less room for other active ingredients and complicating the development of concentrated powders. Moreover, precursor systems do not bleach very efficiently in countries where consumers have wash habits entailing low dosage, short wash times, cold temperatures and low wash liquor to substrate ratios.
Alternatively, or additionally, hydrogen peroxide and peroxy systems can be activated by bleach catalysts, such as by complexes of iron and the ligand MeN4Py (i.e. N,N-bis(pyridin-2-yl-methyl)-bis(pyridin-2-yl)methylamine) disclosed in WO95/34628, or the ligand Tpen (i.e. N,N,Nxe2x80x2,Nxe2x80x2-tetra(pyridin-2-yl-methyl)ethylenediamine) disclosed in WO97/48787.
As discussed by N. J. Milne in J. of Surfactants and Detergents, Vol 1, no 2, 253-261 (1998), it has long been thought desirable to be able to use atmospheric oxygen (air) as the source for a bleaching species. The use of atmospheric oxygen (air) as the source for a bleaching species would avoid the need for costly peroxyl generating systems. Unfortunately, air as such is kinetically inert towards bleaching substrates and exhibits no bleaching ability. Recently some progress has been made in this area. For example, WO 97/38074 reports the use of air for oxidising stains on fabrics by bubbling air through an aqueous solution containing an aldehyde and a radical initiator. A broad range of aliphatic, aromatic and heterocyclic aldehydes is reported to be useful, particularly para-substituted aldehydes such as 4-methyl-, 4-ethyl- and 4-isopropyl benzaldehyde, whereas the range of initiators disclosed includes N-hydroxysuccinimide, various peroxides and transition metal coordination complexes.
However, although this system employs molecular oxygen from the air, the aldehyde component and radical initiators such as peroxides are consumed during the bleaching process. These components must therefore be included in the composition in relatively high amounts so as not to become depleted before completion of the bleaching process in the wash cycle. Moreover, the spent components represent a waste of resources as they can no longer participate in the bleaching process.
The recent development of air bleaching using O2 bleaching catalysts has provided an effective bleach composition that does not rely on peroxygen bleach or a peroxy-based or peroxyl-generating bleach system. One significant advantage of these recent developments is that the oxygen in the air is provided free.
Presently, oxygen bleaching catalysts per se are more selective in bleaching oily stains, for example tomato stains than polar stains, for example tea. It would be advantageous to provide an air bleaching composition that is effective on both oily and polar stains. In addition, it would be advantageous to provide a bleaching composition that contains a reduced amount of peroxyl or peroxyl generating system per wash dose.
We have now found that it is possible to achieve a bleaching composition that has a broad stain bleaching ability, for example, bleaching of both oily tomato and tea type stains.
Catalysts of the present invention catalyse bleaching of stains with either oxygen or peroxy species. An object of the present invention is to provide a bleaching composition that allows bleaching in a single wash with both oxygen and a hydroperoxy species in the presence of a catalyst, i.e., dual bleaching. The dual bleaching is achieved by an aqueous solution of a bleaching composition in which oxygen competes with a peroxyl species for interaction with an oxygen bleaching catalyst. The concentration of peroxyl species that is provided by a unit dose allows oxygen bleaching to compete in an aqueous wash.
When a peroxyl species is present in a dominant concentration in an aqueous solution of an oxygen bleaching catalyst the reaction of oxygen with the oxygen bleaching catalyst is suppressed. One factor that is difficult to change in an aqueous solution is the low solubility of oxygen in water. The concentration of oxygen in water is relatively low when compared to organic solvents. The oxygen concentration in water is approximately 0.2 mM at 20xc2x0 C. and the solubility of oxygen in water decreases about 15% per 10xc2x0 C. increase in temperature of the water as detailed in The Handbook of Chemistry and Physics, 72nd Edition, CRC press. Hence, the oxygen concentration in water at 40xc2x0 C. is approximately 0.15 mM. In order, for oxygen in an aqueous solution to compete with a peroxyl species, the concentration of the peroxyl species has to be substantially below conventional concentrations of between 5 and 10 mM that are found in aqueous wash mixtures. Throughout the disclosure and claims the description of oxygen concentration refers to the concentration of oxygen dissolved in an aqueous environment unless otherwise specified.
Alternatively, dual bleaching is achieved in a stepwise fashion by changing from oxygen bleaching to hydroperoxy bleaching during the course of an aqueous wash. The stepwise bleaching may be achieved in the following manner. 1) Initially bleaching with oxygen followed by raising the concentration of a peroxyl species present. 2) Reducing the concentration of peroxyl species in the wash such that oxygen bleaching is effective.
In contrast to having a limited amount of a hydroperoxy species present in a wash the bleaching composition may contain an agent for decomposing hydrogen peroxide during a wash cycle. Initially during a wash hydrogen peroxide acts as the main bleaching agent in conjunction with a catalyst but as the wash proceeds a hydrogen peroxide decomposing agent is released into the wash. The hydrogen peroxide decomposing agent decomposes hydrogen peroxide into water and oxygen thereby reducing the hydrogen peroxide concentration in the wash. A consequence of reducing the hydrogen peroxide concentration in the wash is that oxygen dissolved in the wash can compete for the catalyst. It is most likely that amounts of the oxygen generated from decomposition of hydrogen peroxide will end up in solution in the wash and participate in the oxygen catalysed bleaching process. A particular benefit of generating hydrogen peroxide in solution is that some gasses other than oxygen in solution, for example nitrogen, will be displaced by the oxygen generated in situ. A beneficial consequence is that the oxygen concentration in an aqueous wash mixture may well exceed 0.2 mM. Oxygen makes up approximately 20% of air and the maximum concentration of oxygen in water at standard temperature and pressure (STP) is about 1 mM. A concentration of oxygen above 0.2 mM would serve to facilitate oxygen bleaching. The catalase enzyme/catalase enzyme mimics provide a suitable class of enzymes for decomposing hydrogen peroxide.
The present invention provides an oxygen-peroxyl competing bleaching composition for use in an aqueous wash medium for bleaching a substrate, the oxygen-peroxyl competing bleaching composition comprising:
(i) an organic substance which forms a complex with a transition metal, the complex for catalysing bleaching of the substrate by atmospheric oxygen in the aqueous medium; and,
(ii) a peroxyl bleaching agent selected from the group consisting of: a peroxyl species and a peroxyl species precursor, for bleaching the substrate in the aqueous medium,
wherein application of a unit dose of the oxygen-peroxyl competing bleaching composition to an aqueous medium provides a concentration of peroxyl species that permits dual bleaching during a wash.
The peroxy species may further be activated by the complex or react with a peroxy acid precursor to yield a peroxy acid.
The present invention extends to a method of bleaching a substrate in an aqueous solution during a wash which comprises the steps of:
providing a concentration of a peroxyl species in the aqueous solution for bleaching tea type stains optionally with a transition metal catalyst that further activates the hydrogen peroxide and/or optionally with a peroxy acid precursor to yield a peroxy acid
providing an amount of oxygen bleaching catalyst to the wash together with oxygen dissolved in the aqueous solution;
reducing the concentration of peroxyl species in the aqueous solution for increasing the amount of oxygen bleaching catalyst available for oxygen bleaching.
In this method oxygen competes with a peroxyl species that is released into an aqueous medium over the course of a wash. In the beginning of a laundry wash the dominant bleaching effect is from oxygen bleaching but as the wash proceeds the concentration of a peroxyl species increases. The increase in peroxygen species suppresses and eventually predominates over oxygen bleaching. It is preferred that the wash is at a temperature of between 10xc2x0 C. and 45xc2x0 C., most preferably between 20xc2x0 C. and 40xc2x0 C.
In this method it is preferred that in the aqueous medium the [oxygen species-complex]/[peroxyl species-complex] is between 10 and 0.1 at a point in time during the wash.
As one skilled in the art will appreciate catalytic mechanisms are complicated. In a particular transformation there may be more than a single pathway or mechanism involved. Presently it is not certain if the xe2x80x9coxygen catalystsxe2x80x9d function by forming an oxygen species-complex/peroxyl species-complex or activate the stain such that activated stain reacts with oxygen/peroxyl. To avoid an overly pedantic analysis of particular concentrations of species the following is provided. In the disclosure and claims the term [peroxyl species-complex] indicates a concentration. The mechanism of bleaching a stain with peroxyl and the complex is not well understood; it is likely that peroxy activation and/or stain activation is taking place. It is possible that this complex forms an active species with peroxyl and that this active peroxyl species-complex bleaches the stain. Alternatively, it is possible that the complex activates a stain such that the activated stain reacts with the peroxyl. In light of the above, one skilled in the art will appreciate that the term [peroxyl species-complex] reflects the concentration of peroxyl used in of the action of the complex in a wash at any given time. The term [peroxyl species-complex] should be construed as such.
In the disclosure and claims the term [oxygen species-complex] indicates a concentration. The mechanism of bleaching a stain with oxygen and the complex is not well understood; it is likely that it is possible that oxygen activation and/or stain activation is taking place. It is possible that this complex forms an active species with oxygen and that this active oxygen species-complex bleaches the stain. Alternatively, it is possible that the complex activates a stain such that the activated stain reacts with the oxygen. In light of the above, one skilled in the art will appreciate that the term [oxygen species-complex] reflects the concentration of oxygen used in of the action of the complex in a wash at any given time. The term [oxygen species-complex] should be construed as such. Consideration of the [oxygen species-complex]/[peroxyl species-complex] is important because the ratio of the rate of depletion of oxygen and a particular peroxy species may vary for a particular catalyst. Nevertheless, it is possible that the rate of depletion of oxygen and a particular peroxy species may not vary significantly for most oxygen bleaching catalysts. In this regard, the ratio [O2]/[total active peroxyl species present] in a wash is useful in defining the invention. The [total active peroxyl species present] represents the concentration of peroxyl species present in solution that is available for bleaching in contrast to a concentration of a peroxyl precursor which is not immediately available for bleaching. As one skilled in the art will appreciate washes are usually conducted in a basic aqueous environment at a pH of approximately 10. Hence, when only hydrogen peroxide is present as a peroxyl bleaching species [total peroxyl present]=[H2O2]+[HOOxe2x88x92]. In a similar manner, when only a peroxyacid is present as a peroxyl bleaching species [total peroxyl present]=[RC(O)OOH]+[RC(O)OOxe2x88x92]. When a mixture of hydrogen peroxide and peroxyacid are present [total peroxyl present]=[RC(O)OOH]+[RC(O)OOxe2x88x92]+[H2O2]+[HOOxe2x88x92]. It is preferred that: [O2]/[total peroxyl present] is in the range 10 and 0.1, which is indicative of a [total peroxyl present] of approximately between 2 mM and 0.02 mM.
The present invention provides differing scenarios for dual bleaching in the presence of an oxygen bleaching catalyst.
1. In a wash, initially approximately 0.2 mM O2 is present and then a peroxyl species is provided in solution such that the peroxyl species dominates the bleaching activity of the wash, for example between 5 and 10 mM peroxyl species.
2. In a wash, initially between 5 to 10 mM hydrogen peroxide is present with approximately 0.2 mM oxygen after which a catalase or a catalase mimic is provided that decomposes the hydrogen peroxide present. The oxygen provided by the decomposed hydrogen peroxide participates on the oxygen bleaching in conjunction with atmospheric oxygen.
3. In a wash, both a peroxyl species and oxygen are initially present in competing concentrations.
In addition to the teachings above the use of a drying step, most preferably in a heated agitated environment as for example found in a tumble dryer has also been found to accelerate and enhance the air bleaching effect. The enhancement may be provided with or without competing amounts of a peroxyl species present.